The Impetrible Blacksmith NPC is located in the Sanctum. You can reach this area through the Warper NPC's under Towns.
Walk north to the center of the map and you will see 4 NPC's. The Impetrible Blacksmith is one of them.
The Impetrible Blacksmith is where you will craft Legendary weapons and other items added over time
such as armor sets, and headgears. The Black BAW will be your first Headgear crafting quest. You will want to grind and craft as many Black BAW as possible because you will need 1 black BAW for each Legendary weapon along with new Stones/Gems just added with the 1.1 patch!